And yet the era of the small car is upon us. Shrinking a car isn't the only way to improve fuel efficiency and reduce emissions. In this week's international edition of "Newsweek," Amory Lovins argues that a whole range of lighter construction materials can perform the same feat on larger vehicles. In fact, reducing weight improves a car's safety. The trouble with the NHTSA study is that it only examined cars that were involved in crashes. Lightweight vehicles tend to be more nimble than heavier cars and can therefore evade accidents more readily in the first place. This is why weight is the enemy in race car design.

We tend to assume that weight and size go hand in hand. And to be sure, the easiest way for an automaker to shed a vehicle's girth is to shrink it. At least, it's the cheapest way. Light, but strong materials such as carbon fiber remain prohibitively expensive, though some high-end automakers are beginning to use it on roofs, hoods and the like. The Smart ForTwo uses plastic door panels, which don't ding or scratch. Inside the door are reinforced steel bars, which provide greater protection for side impact, yet weigh less than conventional car doors.

Sales of small cars are indeed climbing in the U.S., though far slower than in the rest of the world. The Big Three, in particular, have resisted pushing small cars. After all, the Yaris and the Fit outsell any American subcompact. Consumers will indeed pay more for big, lightweight cars. But if Americans truly refuse to give up size, car makers should bite the bullet. Find new ways to lose weight.